This invention relates to a phase plug structure which serves as a phase equalizing means in a loudspeaker system. In a typical system using an exponential horn, a compression chamber located between the speaker diaphragm and the horn transfers energy between these elements. Typically, to reduce distortion, the surface area of the diaphragm is relatively large compared to the cross-sectional area of the horn throat. The size difference causes acoustic waves from the center of the diaphragm to reach the throat of the horn before vibrations from the periphery of the diaphragm which must travel across the compression chamber before reaching the horn. This causes the acoustic vibrations from the various portions of the diaphragm to have phase differences between them. These phase differences can result in phase cancellations at particular frequencies, thereby limiting the high-frequency response of the compression horn transducer. Use of phase plugs having annular rings therein which equalize the path lengths between the various portions of the diaphragm and the horn is one means of minimizing these phase cancellations.